Dynamic channel quality measurement procedure implemented in a wireless digital communication system to prioritize the forwarding of downlink data

ABSTRACT

A wireless digital communication system includes a base station in communication with a plurality of user equipment mobile terminals (UEs). The system prioritizes the forwarding of blocks of downlink data to designated ones of the UEs. The system employs adaptive modulation and coding (AM&amp;C) to achieve improved radio resource utilization and provides optimum data rates for user services. Blocks of downlink (DL) data are received by the base station which requests downlink (DL) channel quality measurements only from those mobile terminals (UEs) with pending downlink transmissions. The UEs respond to the request by measuring and reporting DL channel quality to the base station, which then allocates resources such that the UEs will make best use of radio resources. The base station notifies the UEs of the physical channel allocation indicating the modulation/coding rate and allocated slots followed by transmission of blocks of downlink data which are transmitted to the UEs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/648,470, filed Dec. 29, 2009, which is a continuation of Ser. No.11/656,647, filed Jan. 23, 2007, now U.S. Pat. No. 7,639,989, which is acontinuation of Ser. No. 10/768,312, filed Jan. 30, 2004, now U.S. Pat.No. 7,171,163, which is a continuation of U.S. patent application Ser.No. 10/029,569, filed Dec. 21, 2001, now U.S. Pat. No. 6,810,236, whichclaims the benefit of U.S. Provisional Patent Application No.60/290,877, filed May 14, 2001, which applications are incorporatedherein by reference.

BACKGROUND

The present invention relates to wireless digital communication systems.More particularly, the present invention relates to communicationstations which employ code-division multiple access (CDMA) technology.Specifically, the present invention relates to determining radioconditions for use in optimizing radio resource utilization as well asselecting data rates for user services.

In code-division multiple access (CDMA) third generation (3G) cellulartelecommunication systems, adaptive modulation and coding (AM&C)techniques are applied to transmissions in order to achieve improvedradio resource utilization and provide increased data rates for userservices under appropriate conditions. These AM&C techniques take intoaccount radio conditions in advance of transmissions in order todetermine modulation and coding rates that take the greatest advantageof current radio propagation conditions utilizing these techniques.

Utilizing these AM&C techniques, a procedure is required that provides aphysical channel quality measurement from the receiver in advance ofeach transmission. Based on this quality measurement, the transmitterdetermines the appropriate modulation and coding rate for the particulartransmission.

In CDMA systems, as with any wireless systems, radio conditions canchange rapidly due to a wide variety of both natural and man-madeconditions. Since the channel quality measurement is used to determinetransmission modulation and coding, and since channel quality changesrapidly due to the changing conditions of the transmission path, theperformance of the adaptive transmission process is directly related tothe length of the time period between when the channel qualitymeasurement is performed and when the transmission is initiated.

Physical or logical control channels are then used to transfer thechannel quality measurements from the receiver to the transmitter.Channel quality signaling may utilize either dedicated control channelsto each user equipment (UE) or common control channels shared by allUEs. A UE may be a cellular phone, PDA (personal data assistant) or anyother type of wireless device. When dedicated control channels are used,a continuous signaling channel is available over time for propagation ofchannel quality measurements for each UE. This is an optimal solutionfor AM&C since the quality measurement is continuously available.Transmissions can occur at any time, taking into account thecontinuously available quality measurement for appropriate modulationand coding settings. Additionally, with a dedicated control channelalways available in the uplink, the channel can be also used to supportlow rate uplink data transmissions.

The difficulty with the dedicated control channel approach is thatphysical resources are continuously allocated even when there is no datato transmit. A primary application of AM&C techniques is non-real timehigh data rate services, for example, Internet access. For these classesof service, the best quality of service (QoS) is achieved with short,high rate transmissions with relatively long idle periods between eachtransmission. These long idle periods result in an inefficient use ofdedicated resources.

The problem can be minimized with pre-configured periodic dedicatedchannel allocations. But this results in periodic availability ofquality measurements. If the quality measurements are not continuouslyavailable, for UEs which have transmissions at any one point in time,only some portion of the UEs will have recent channel qualitymeasurements.

Another alternative is the use of common control channels. With commoncontrol channels, a continuous signaling channel exists that is sharedbetween all UEs within the cell. Procedures are defined for determiningeach UEs access to the common control channel. UE identities are used todistinguish UE specific transactions.

The difficulty with the common control approach for support of AM&C isthe large amount of signaling overhead necessary to administrate eachUE's access to the control channel. As aforementioned, UE identities arerequired to distinguish UE specific transactions. Additionally, to avoidcontention-based access to the uplink common control channel, individualallocations are required to be signaled on the downlink common controlchannel for each UE's access. Since uplink transmissions cannot alwaysbe predicted, periodic allocations of the uplink control channel must besignaled on the downlink common control channel, which results inconsiderable signaling overhead. Also, the common control approach doesnot provide for low rate, uplink data transmissions.

In summary, the efficient performance of AM&C techniques is primarilybased on the availability of recent physical channel qualitymeasurements from the receiver in advance of each transmission.Optimally, measurements are available with minimal latency for all userswith active data transmissions. The dedicated control channel solutionprovides continuous measurements, but since transmissions arediscontinuous, this is an inefficient use of radio resources. Periodicconfigured dedicated control channels minimize the radio resourcerequirement, but this increases measurement latency. The common controlchannel method can provide measurements on a continuous or periodicbasis, but the signaling overhead results in an inefficient use of radioresources.

There exists a need for a system that provides channel qualitymeasurements with low latency and low signaling overhead.

BRIEF DESCRIPTION OF THE DRAWING(S)

The objectives of the present invention will become apparent uponconsideration of the accompanying detailed description and figures, inwhich:

FIG. 1 is a flow chart illustrating one preferred Dynamic ChannelQuality Measurement Procedure (DCQMP) of the present invention.

FIG. 2 shows an alternative embodiment of the DCQMP of the presentinvention shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Presently preferred embodiments are described below with reference tothe drawing figures wherein like numerals represent like elementsthroughout.

FIG. 1 is a flow diagram which illustrates the dynamic channel quality(CQ) measurement procedure 60 of the present invention which may beimplemented by a wireless digital communication system having a basestation/node B (hereinafter base station 12) which communicates with atleast one UE 30. Although it is intended for the presently inventivemethod to support communications between a base station and a pluralityof UEs, for simplicity the following description will detail the stepsperformed by a single UE, it being understood that other UEs willoperate in a similar manner.

Blocks of downlink (DL) data are transferred to the base station 12which are designated for a particular UE 30 (step S1).

The base station 12, responsive to receipt of downlink data and inadvance of a transmission to the UE 30, requests DL CQ measurements onlyfrom a UE 30 having pending downlink transmissions (step S2).

The UE 30 receives the request and makes the requested CQ measurement atstep S3 and reports the DL CQ measurement to the base station 12 at stepS4.

Based on the CQ measurement reports received from each UE (step S5), thebase station 12 determines which of the UEs will make the best use ofradio resources, and determines which slots to use (step S6).Preferably, the UEs are prioritized by their CQ so that the UE with thehighest CQ is sent its data first and then the UE with the secondhighest CQ is sent its data second, and so on until the UE with thelowest CQ is sent its data last.

Since the CQ measurement requests and the responsive CQ measurementreports are only generated when needed, the signaling overhead requiredfor a common control channel is greatly reduced. Measurement reports areavailable for all active transmitting users, similar to the dedicatedcontrol channel case, but avoiding the resource inefficiency during idleperiods.

The priority of transmissions is determined according to the DL CQmeasurements, and the DL physical channel allocation is signaled to theappropriate UEs, indicating the particular coding rate, modulation typeand allocated slots (step S7). The designated UE receives the codingrate, modulation type and allocated slots (step S8), and sets theseparameters for reception (step S9).

Blocks of downlink data are then transmitted by the base station 12 tothe designated UE 30 (step S10) a given, but short, time afterperformance of step S7 to enable the UE 30 time to set up for reception.The UE 30 receives the downlink data (step S11) at the specified codingrate, modulation type and in the allocated slots specified at step S7.

The present invention thus provides the fundamental requirements forAM&C operation while maintaining the most efficient use of radioresources. Since DL CQ measurements are available with the minimumpossible latency for all transmissions, the choice of the best user(s)to provide service in the next transmission time frame is optimized.Additionally, measurements provided by periodic or continuous mechanismsdo not provide increased benefit, performance gain or enhancement overthe present invention.

Implementation of the present invention also minimizes measurementprocessing and the associated power consumption, especially important inthe UE, which is typically powered by a small power source of limitedcapacity, (i.e. a chargeable battery). Since a quality measurement isonly requested for a particular active transmission, the number ofrequired measurements are minimized.

In accordance with an alternative embodiment of the method 70 of thepresent invention shown in FIG. 2, only certain quality measurements maybe required depending on the radio resources used for a particulartransmission. For example, in the 3G standards, the CQ for only specificphysical timeslots may be requested. Therefore, the number ofmeasurements performed is reduced by limiting the requirement of a CQmeasurement to only active transmissions and, depending on the scale ofthe transmission, only requiring measurement on particular radioresources, (i.e., specific time slots). This is shown in FIG. 2, whichis similar to FIG. 1 except for modified steps S2A and S3A, whichreplace steps S2 and S3 respectively of FIG. 1. In step S2A, the basestation 12 requests the UE 30 to perform a measurement only on aparticular radio resource. In response, the UE performs the DL CQmeasurement on the specified radio resource (step S3A).

The present invention provides many advantages over prior art schemes.First, the invention provides the highest efficiency utilization of theair interface since only those UEs having pending transmissions will berequired to respond to a request for DL CQ measurements. This permitsthe overhead signaling to be at a minimum.

Second, since the transmissions are prioritized according to the highestquality DL CQ measurements, the highest data rates permissible will beachieved for each time slot or multiple time slots.

Third, since UEs are only required to respond to the request for the DLCQ measurements, unnecessary measurements by the UEs will not berequired, thereby saving the battery life of the UEs.

A final advantage of the present invention is the increased number ofusers that may be supported in a cell for both of the methods disclosedherein. The number of users that are supported is limited in thededicated control channel method by the requirement for dedicated radioresources; and in the common control channel method by signalingoverhead requirements. By limiting the measurement signaling proceduresto active users, the present invention minimizes the common controlsignaling overhead and supports the greatest number of users in thecell.

While the present invention has been described in terms of the preferredembodiment, other variations which are within the scope of the inventionas outlined in the claims below will be apparent to those skilled in theart.

1. A method of for requesting channel quality measurement report, themethod comprising: transmitting at least one request to provide achannel quality (CQ) measurement report; receiving a CQ measurementreport in response to the request; transmitting an allocation of radioresources that is based on the transmitted CQ measurement report; andtransmitting downlink data in accordance with the allocation of radioresources.
 2. The method of claim 1 wherein the allocation of radioresources includes at least one of a coding rate and a modulation type.3. The method of claim 1 wherein the at least one request to provide aCQ measurement report is transmitted over a common control channel or adedicated control channel.
 4. The method of claim 1 wherein the at leastone request to provide a CQ measurement report indicates at least oneparticular radio resource upon which the corresponding CQ measurement isto be based.
 5. A base station comprising: a transmitter configured totransmit at least one request to provide a channel quality (CQ)measurement report; a receiver configured to receive a CQ measurementreport in response to the request; and the transmitter furtherconfigured to transmit an allocation of radio resources that is based onthe transmitted CQ measurement report, and to transmit downlink data inaccordance with the allocation of radio resources.
 6. The base stationof claim 5 wherein the allocation of radio resources includes at leastone of a coding rate, and a modulation type.
 7. The base station ofclaim 5 wherein each of the at least one request to provide a CQmeasurement report is transmitted over a common control channel or adedicated control channel.
 8. The base station of claim 5 wherein eachof the at least one request to provide a CQ measurement report indicatesat least one radio resource upon which the corresponding CQ measurementreport is to be based.
 9. A method for transmitting downlink controlinformation to at least one user equipment (UE), the method comprising:transmitting by a base station a request to provide a channel quality(CQ) measurement report; receiving by the base station a CQ measurementreport in response to the request; transmitting by the base stationdownlink control information including an allocation of resources,wherein the downlink control information is distinguished by a UEidentity (ID) associated with a specific UE; and transmitting by thebase station downlink data in accordance with the allocation of radioresources.
 10. The method of claim 9 wherein the allocation of radioresources includes at least one of a coding rate and a modulation type.11. The method of claim 9 wherein the request to provide a CQmeasurement report is transmitted over a common control channel or adedicated control channel.
 12. The method of claim 9 wherein the requestto provide a CQ measurement report indicates at least one particularradio resource upon which the CQ measurement is to be based.
 13. Themethod of claim 9 wherein the allocation of radio resources is based onthe received CQ measurement report.
 14. A base station comprising: atransmitter configured to transmit a request to provide a channelquality (CQ) measurement report; a receiver configured to receive a CQmeasurement report in response to the request; and the transmitterfurther configured to transmit UE downlink control information to a UEincluding an allocation of resources, wherein the downlink controlinformation is distinguished by a UE identity (ID) associated with theUE, and to transmit downlink data in accordance with the allocation ofradio resources.
 15. The base station of claim 14 wherein the allocationof radio resources includes at least one of a coding rate, and amodulation type.
 16. The base station of claim 14 wherein the request toprovide a CQ measurement report is transmitted over a common controlchannel or a dedicated control channel.
 17. The base station of claim 14wherein the request to provide a CQ measurement report indicates atleast one radio resource upon which the CQ measurements report is to bebased.
 18. The base station of claim 14 wherein the allocation of radioresources is based on the received CQ measurement report.